1. Field of the Invention
The field of this invention relates to polyimides prepared from tetramethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride (TMCDA) and diamines. These novel polyimides are useful in preparing molded articles, fibers, laminates and coatings.
2. Background
It is known to make polyimides from pyromellitic dianhydride and aromatic diamines. This is disclosed in U.S. Pat. No. 3,179,634 (1965). British Patent Specification No. 570,858 discloses various processes for making fiber forming polymers. The Japanese Patents listed below disclose the preparation of polyimides starting with cyclobutane-1,2,3,4-tetracarboxylic dianhydride.
JA 7123917-S27, JA 7137733-S44, JA 7137734-S44, JA 7219710-T23, and JA 72199098-T23. The article by F. Nakanishi and M. Hasegawa, Polymers, 14, 440 (1973) discloses the use of cyclobutane-1,2,3,4-tetracarboxylic dianhydride and 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride in the preparation of polyimides. In reviewing all these references, it is clear that the use of TMCDA to form polyimides useful as moldings, fibers, laminates, and coatings has not been contemplated in the prior art.
The general object of this invention is to provide novel polyimides based on TMCDA and diamine moieties. A more specific object of this invention is to provide polyimides from TMCDA moieties and aliphatic, cycloaliphatic, araliphatic and aromatic moieties. Another object is to provide a process for the manufacture of polyimides, from TMCDA and diamines.
We have found that novel polyimides can be formed by reacting TMCDA with diamines. TMCDA reacts readily with the diamine to form a high molecular weight polyimide. In this process both aliphatic and aromatic diamines can be polymerized with TMCDA to form high molecular weight polyimides.
Our process for the manufacture of the novel polyimides comprises reacting about equal molar amounts of TMCDA with a primary diamine. The molar ratio of TMCDA to the primary diamine may be in the range of 1.2:1 to 1:1.2, preferably in the range of 1 to 1. In suitable method, the reaction is conducted as a batch reaction at a temperature of about 130.degree. to 300.degree. C. for a period of about 2 to 24 hours in a nitrogen containing organic polar solvent such as 1-methyl-2 pyrrolidinone (NMP), N,N-dimethylacetamide, N,N-dimethylformamide or pyridine. The polycondensation can also be carried out as a continuous process. The polycondensation can suitably be carried out at a temperature of 130.degree. C. to 300.degree. C., preferably at a temperature of 180.degree. to 200.degree. C. The water by-product in these reactions may be distilled off at 100.degree.-150.degree. C., removed by a stream of nitrogen or azeotroped with an organic solvent such as xylene. The polymerization reaction can also be carried out in the melt under an inert atmosphere or in vacuum. The novel polyimides of this invention have the following recurring structure wherein R is a divalent aliphatic or aromatic hydrocarbon radical. ##STR1## The radical R may be divalent aliphatic hydrocarbons of 2 to 18 carbon atoms or an aromatic hydrocarbon from 6 to 20 carbon atoms, or an aromatic hydrocarbon radical containing from 6 to 10 carbon atoms joined directly or by stable linkage comprising --O--, methylene, ##STR2## --SO--, --SO.sub.2 --, and --S-- radicals. The radical R is derived from aliphatic, araliphatic or cycloaliphatic diamines such as ethylenediamine, propylenediamine, 2,2-dimethylpropylenediamine, tetramethylenediamine, hexamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 4,4'-diaminodicyclohexylethane, xylylene diamine and bis (aminomethyl) cyclohexane. Suitable aromatic diamines useful in Applicant's process include para and meta-phenylenediamine, 4,4'-oxydianiline, thiobis (aniline), sulfonylbis (aniline), diaminobenzophenone, methylenebis (aniline), benzidine, 1,5-diaminonaphthalene, oxybis (2-methylaniline), thiobis (2-methylaniline), and the like. Examples of other useful aromatic primary diamines are set out in U.S. Pat. Nos. 3,494,890 (1970) and 4,016,140 (1972) both incorporated herein by reference. The preferred diamines are 1,6-hexanediamine, 1,12-dodecanediamine and 4,4'-oxydianiline.
In some cases the polyimide may be further polymerized under "solid state polymerization" conditions. The term solid state polymerization refers to chain extensions of polymer particles under conditions where the polymer particles retain their solid form and do not become a fluid mass. The solid state polymerization can be carried out below the melting point of the polyimide and can be conducted in several ways. However all techniques require heating the ground or pelletized polyimide below the melting point of the polyimide, generally at a temperature of about 200.degree. to 300.degree. C. while either sparging with an inert gas such as nitrogen or operating under vacuum. In cases where the polyimides have a low melt temperature, they can be polymerized in the melt under vacuum in thin sections or using thin film reactors known in the art.
Injection molding of the novel polyimide is accompanied by injecting the polyimide into a mold maintained at a temperature of about 50.degree. to 150.degree. C. In this process a 20 second to 1 minute cycle is used with a barrel temperature of about 200.degree. to 350.degree. C. These temperatures will vary depending on the T.sub.g and T.sub.m of the polymer being molded.
The novel polyimides have excellent mechanical and thermal properties and can readily be molded into useful articles or formed into fibers, films, laminates or coatings. The physical tensile properties of the polyimide made with 1,12-dodecanediamine and the glass-reinforced polyimide are shown on Table 2. Infrared spectra of the polyimides have confirmed the polyimide structure.
Analysis of the TMCDA-diamine polyimide by thermal gravimetric analysis shows excellent stability. This is demonstrated by the fact that under nitrogen atmosphere 1% weight loss occurs at a temperature of about 300.degree. C. and the main weight loss occurs at a temperature of about 400.degree. C. Glass transition temperature T.sub.g of the polyimide varied with the particular diamine used as shown in the Examples. Values range from a T.sub.g of 60.degree. C. to 285.degree. C.
Diamines with the amino groups attached directly to the aromatic ring are suitably polymerized with TMCDA by solution condensation in organic polar solvents. Useful polar solvents include N,N-dimethylacetamide, 1-methyl-2-pyrrolidinone, N,N-dimethylformamide, pyridine, and the like.
We have found that the polyimides of this invention are improved by the addition of reinforcing material particularly the mechanical properties of the polyimides are improved if these polyimides contain from about 25 to 60 percent by weight glass fibers, glass beads, or graphite or mixtures thereof. In the preferred range the polyimides contain 30 to 40 percent by weight of the glass fibers, glass beads, or graphite or mixtures thereof. Suitably reinforcing materials can be glass fibers, glass beads, glass spheres, glass fabrics. The glass fibers are made of alkali-free boron-silicate glass or alkali containing C-glass. The thickness of the fiber is suitably on the average between 3 mm and 30 mm. It is possible to use both long fiber with average lengths of from 5 to 55 mm and also short fibers with an average filament length from 0.05 to 5 mm. In principle, any standard commercial-grade fibers especially glass fibers may be used. Glass beads ranging from 5 mm to 50 mm in diameter may also be used as a reinforcing material.
The reinforced polyimide polymers may be prepared in various ways. For example, so-called rovings endless glass fiber strands are coated with the polyamic acid and subsequently granulated. The cut fibers or the glass beads may also be mixed with polyamic acid solution and heated to form the reinforced polyimide. Injection molding of the novel glass-filled polyimide is accomplished by injecting the polyimide into a mold maintained at a temperature of about 50.degree. to 150.degree. C. In this process a 20 second cycle is used with a barrel temperature of about 200.degree. to 300.degree. C. The injection molding conditions are given in Table 1.
TABLE I ______________________________________ Mold Temperature 50 to 150.degree. C. Injection Pressure 15,000 to 19,000 psi and held for 1 to 3 seconds Back Pressure 100 to 220 psi Cycle Time 20 seconds Extruder: Nozzle Temperature 200 to 350.degree. C. Barrels: Front heated to 200 to 350.degree. C. Screw: 20 to 25 revo- lutions/minute ______________________________________
The mechanical properties of the polyimide of the glass reinforced polyimides are given in Table 2, and show that these polyimides have excellent mechanical and thermal properties.